This invention relates to a process of exhaust gas aftertreatment by secondary injection of fuel in a diesel internal combustion engine with precatalyst and particulate filter.
Use of a particulate filter to effectively reduce particulate emissions by a diesel engine effectively will be unavoidable in the future. Because of low exhaust gas temperatures, the filter is constantly charged with soot, something which in the extreme case can result in breakdown of a vehicle, especially in the event of repeated short-distance operation.
Document EP 0 621 400 A 1 discloses an air compressing internal combustion injection engine with exhaust gas aftertreatment equipment. A reducing agent may be fed to this internal combustion injection engine in order to reduce nitrogen oxides. The reducing agent is prepared in the final stage of combustion downstream from the ignition OT by secondary injection of fuel.
In addition, document DE 197 35 011 A 1 discloses a process in which exhaust gas temperature dependent and time dependent secondary fuel injection is prepared for the purpose of nitrogen oxide reduction. For this purpose transition is made from a first secondary injection mode to a second secondary injection mode involving a secondary injection amount higher than in the first mode.
Secondary injection or afterinjection of fuel in each instance serves the purpose of raising the exhaust gas temperature by means of an exothermal reaction which takes place within a specific exhaust gas temperature range; however, temperature alone does not represent a suitable criterion for effective secondary injection of fuel.